This is called "light bleeding" and happens with automatic atlas-mapping. I think this can happen if you compile your level into a single mesh with one uv-map. The borders of the single faces in the uv-map are probably too small and there is no room for overlapping of some colors over the borders of their uv-faces.

The Atlas-Mapper in Lightwave takes all that into account but I think the Gamestudio lightmapper still has those issues. I think only Conitec can help in this case. Mr. Stolipin has to re-work the light-mapper to prevent such problems.